class Animal(object):
    def __init__(self,classname='Animal'):
        self.__classname = classname
    def run(self):
        print('{} is running...'.format(self.__classname))


class Dog(Animal):
    def __init__(self):
        Animal.__init__(self,classname='Dog');

class Cat(Animal):
    def __init__(self):
        Animal.__init__(self,classname='Cat');

dog = Dog()
dog.run()
#输出：#Dog is running...
cat = Cat()
cat.run()
#输出：#Cat is running...


